This invention relates to glass fiber production and, more particularly, to an improved microcomputer controlled winder for attenuating a plurality of streams of molten glass into fibers and for collecting the fibers as a strand on a wound package.
One method for manufacturing textiles from glass involves attenuating a plurality of streams of molten glass into fibers, collecting the fibers into a strand and winding the strand into a package for subsequent use in manufacturing various products. The molten glass initially flows at a controlled rate from a furnace forehearth into a feeder or bushing which has a plurality of orifices formed in its bottom. As the molten glass flows from the orifices, it is pulled downwardly at a high rate of speed for attenuation into fibers. A plurality of the attenuated fibers are then gathered together into a strand, coated with a sizing, and the strand is wound onto a package on a winder collet. The speed of the winder collet is controlled in an attempt to maintain a uniform attenuation speed, which in turn produces a uniform diameter in the attenuated fibers if other conditions such as the temperature of the molten glass remain constant. Since the strand is wound onto a core to form a package, the diameter of the package will gradually increase. As the diameter increases, the rotational speed of the collet must be simultaneously decreased to maintain a constant attenuation rate.
Various controls have been known in the prior art for controlling a winder collet speed for maintaining a substantially uniform attenuation rate as the size of a package on which glass fibers are wound changes. In a typical prior art system, a digital computer or other process controller stores data corresponding to a desired winder collet speed at different predetermined points of time after the start of winding a package. At each of these points of time, the winder collet speed is sampled and compared with the desired speed for generating an error signal. The error signal is used to modify the winder collet speed in order to reduce the deviation between the desired speed and the actual speed. In one prior art system, as illustrated in U.S. Pat. No. 3,471,278 which issued Oct. 7, 1969, the winder speed is controlled by means of a magnetic clutch connecting a constant speed motor to a generator. The output from the generator in turn drives the winder motor. A digital computer generates an output signal which is converted to an analog signal for driving a ramp function generator. The ramp function generator in turn drives the magnetic clutch to warp or ramp down the speed of the winder collet as the diameter of the package increases to maintain a constant fiber attenuation and strand collection speed. In order to change the product collected on the winder, a different analog winder speed ramp curve must be stored in the digital computer.
In addition to a constant attenuation speed, other conditions must be uniform to achieve a uniform fiber diameter throughout a package. For example, the molten glass head within the bushing must remain constant to achieve a constant flow rate through the bushing orifices. Also, the temperature of the molten glass must remain constant to provide a constant viscosity of the molten glass and, therefore, a constant flow rate through the orifices. Ideally, a bushing is continuously operated under steady state conditions. Several winder collets are mounted on a turret. When a package on one winder collet is near completion, the next winder collet is brought up to speed. At the end of the package, the next winder collet is indexed to the winding position and the attenuated fiber strand is picked up and wound onto the second package. By continuous operation of this type, both production is increased and variations in the fiber diameter throughout the package are minimized. The winder collet speed controller automatically ramps down or warps the speed of each successive winder collet as the packages are formed. During this operation, the bushing is maintained at steady state conditions. The glass throughput which enters the bushing from the furnace forehearth and leaves the bushing from the plurality of orifices in the bushing bottom has a predetermined high temperature. In order to compensate for heat losses radiating from the bushing, an electric current is passed through the bushing for maintaining a desired temperature of the bushing and molten glass therein. Through this arrangement, the temperature of the molten glass issuing from the bushing orifices is carefully controlled to provide a uniform fiber diameter. However, for various reasons it is sometimes necessary to shut the bushing down for a short period of time. This may be caused by a break in the fibers forming the strand, for example. The downtime for the bushing may vary from a few minutes up to eight minutes or more, depending the availability of an operator to restart the bushing. During the first few minutes that a bushing is shut down, there is some decrease in temperature of the bushing due to the cessation of glass throughput. When the bushing is restarted, the slightly lower temperature causes an increase in the viscosity of the glass and, therefore, a decrease in the flow rate of the molten glass through the bushing orifices. If the normal attenuation speed is used at this time, it will be apparent that the diameter of the attenuated fibers will decrease. One prior art solution to this problem has been to discard the fibers initially made after a bushing has been shut down.